Mercedes W124 M103 260E

[carat 3.6]

Yesterday- Tuesday i went to stert the car up after 3 days ,and it started right away stumbled, and stopped.But started again right away .. Have a new fuel fiter on its way, it should come to-day. I will get that fitted along with the original accumulator i keep after i fitted a new one 5 years back at the same time the filter was fitted .Get earths checked at the same time . Keep looking in for further news .Mobile thingamabob will be here Thursday to do it.

The way your describing this fault I'm going to say it isnt a blocked filter or any sort of mechanical fault with the fuel system. The fact that it stops and then immediately restarts leads me to believe the fuel pumps are loosing their power.

Knowing what I do about these cars a bad earth for the pumps is possible, but very unlikely.

If your happy that both pumps are working as they should, either the live feed to the pumps is dropping out because of a fault at the relay, or another possibility is that the engine management itself is loosing power.

As this is an intermittent fault if I was going to try to pin it down further I would install some temporary test lights, one at the round plug I mentioned on the live to the pumps and another on the trigger wire to the fuel pump relay. Make sure you can see them from the drivers seat, that will give you an indication of what is happening in real time when the fault occurs.

 

[optimusprime]

carat 3.6. To put you in the picture .Yesterday the mobile mechanic turned up late .Car had sat for 2 days .She would not start with first try , just cranking over .So mechanic could see for himself . But after another few tries fuel must have reached the fuel distributor, and it started up .. We then took the car for a spirited drive .Well it ran very good, better with the new fuel pumps fitted. So to rule out the fuel filter thats in there , i have a new Mercedes fuel filter from Benz of Newcastle . Along with the original fuel accumulator that i keept after i fitted a good used one 8 years ago .So next step is to have these both fitted . I will let the drive queen sit for another day and give her a try again to see if will start . Will return after a day and let you know if it started .​

 

[carat 3.6]

carat 3.6. To put you in the picture .Yesterday the mobile mechanic turned up late .Car had sat for 2 days .She would not start with first try , just cranking over .So mechanic could see for himself . But after another few tries fuel must have reached the fuel distributor, and it started up .. We then took the car for a spirited drive .Well it ran very good, better with the new fuel pumps fitted. So to rule out the fuel filter thats in there , i have a new Mercedes fuel filter from Benz of Newcastle . Along with the original fuel accumulator that i keept after i fitted a good used one 8 years ago .So next step is to have these both fitted . I will let the drive queen sit for another day and give her a try again to see if will start . Will return after a day and let you know if it started .​

If your mechanic wants to change the filter he must be happy that the pumps are running when they should, when was the tank filter last changed?

 

[Bellow]

I really can't see how the filter could affect starting given - relative to driving - the very low fuel flow required. If it can pass enough fuel to drive on the road it can easily pass enough for starting.

The way your describing this fault I'm going to say it isnt a blocked filter or any sort of mechanical fault with the fuel system. The fact that it stops and then immediately restarts leads me to believe the fuel pumps are loosing their power.

The above to me is much more plausible and...

As this is an intermittent fault if I was going to try to pin it down further I would install some temporary test lights, one at the round plug I mentioned on the live to the pumps and another on the trigger wire to the fuel pump relay. Make sure you can see them from the drivers seat, that will give you an indication of what is happening in real time when the fault occurs.

...the above would be my next step.

 

[optimusprime]

Thanks,, yes i know the fuel filer i not to blame ..but as work is being done down under besrt to replace the filter at the ame time.. Filter was fitted in 2014 aprox and i do 3000 miles a year . Now i could not sit hetre ,,i just had to go out and try to start the car again. Well key in, no pumps = no tart . So cycled the key again , no pumps,,so i cycled the key for the third time and the pumps tun on and car started up. Looking now at electrical fault ..

 

[carat 3.6]

Thanks,, yes i know the fuel filer i not to blame ..but as work is being done down under besrt to replace the filter at the ame time.. Filter was fitted in 2014 aprox and i do 3000 miles a year . Now i could not sit hetre ,,i just had to go out and try to start the car again. Well key in, no pumps = no tart . So cycled the key again , no pumps,,so i cycled the key for the third time and the pumps tun on and car started up. Looking now at electrical fault ..

Pull the fuel pump relay out and check for corrosion on the pins of the relay itself, and the board it plugs into. You can remove the individual connections from the board if needed.

You could go further and start testing the control circuit, but I'd bet you have a dry joint in the relay. -Replace the relay.

 

[optimusprime]

carat 3.6. Thank you .... Before pumps were fitted the FPR was swapped over for good original one that came in the car some time ago, so i know its a good one . . So i used jumper lead in 7 and 8 to eliminate FPR .Still no start ,and still no fuel from main feed to FD , but it did start . but for seconds only with Starter Fluid .. . If there is no fuel in the FD then the engine will fail to start due to pressure drop over night , and the pumps wont energise due to no signal to say engine is running ... Same with OVP relay, i changed that for a good one . still did not run , so replaced it with the one i removed .Now after new pumps fitted it started by cycling the key a few times it starts the pumps up ,. .the car goes like stink .Ticks over fine ..Just wont start after a good lie down ...as fuiel pressure is lost .I recon it could just be the Fuel Accumulator.

 

[carat 3.6]

carat 3.6. Thank you .... Before pumps were fitted the FPR was swapped over for good original one that came in the car some time ago, so i know its a good one . . So i used jumper lead in 7 and 8 to eliminate FPR .Still no start ,and still no fuel from main feed to FD , but it did start . but for seconds only with Starter Fluid .. . If there is no fuel in the FD then the engine will fail to start due to pressure drop over night , and the pumps wont energise due to no signal to say engine is running ... Same with OVP relay, i changed that for a good one . still did not run , so replaced it with the one i removed .Now after new pumps fitted it started by cycling the key a few times it starts the pumps up ,. .the car goes like stink .Ticks over fine ..Just wont start after a good lie down ...as fuiel pressure is lost .I recon it could just be the Fuel Accumulator.

I thought the pumps were not running when you turn the ignition on? Just to be clear when you bridged pins 7 and 8 you heard the pumps running continuously?

 

[optimusprime]

carat 3.6 Most of above post was before the new fuel pups were fitted Up till now, because it starts, i had no use to hot wire in 7-8 , we proved pumps are working .But not on the first turn of the key ,i have to cycle the key 2x to hear the pumps kick in ...fuel is running back to the tankas it sits over night . .This stops the engine starting if the FD is void of fuel ,then because engine failed to start signal is switched off .after seconds .Your idea on this ?

 

[carat 3.6]

carat 3.6 Most of above post was before the new fuel pups were fitted Up till now, because it starts, i had no use to hot wire in 7-8 , we proved pumps are working .But not on the first turn of the key ,i have to cycle the key 2x to hear the pumps kick in ...fuel is running back to the tankas it sits over night . .This stops the engine starting if the FD is void of fuel ,then because engine failed to start signal is switched off .after seconds .Your idea on this ?

The engine management system of an m103 will trigger the fuel pump relay briefly to prime the system every time the ignition is switched on, if it doesn't do that every time you have an electrical fault. It will also trigger the fuel pump relay whilst cranking, the starter signal acts as a trigger wire.

The pressure accumulator will help the engine to start quickly, but even if it is faulty the engine should start after a couple of rotations. If you think the fuel is running back to the tank overnight that would indicate an actual leak in the fuel system somewhere, possibly a rust hole in the fuel line itself.

 

[optimusprime]

But if the engine has no fuel, it wont start , and then the message sent will be switched off in seconds... its strange i have just been out to the car and it started and it was instantaneous .

 

[carat 3.6]

But if the engine has no fuel, it wont start , and then the message sent will be switched off in seconds... its strange i have just been out to the car and it started and it was instantaneous .

No. The fuel pump relay will be activated whilst you are cranking the engine, the starter signal keeps it latched.

You need to check:

1. If the pumps prime every time you turn the ignition on.

2. That the pumps are running whilst cranking.

If they are not you either have a fault at the fuel pump relay, or the circuit that turns it on. My bet would be a dry solder joint in the relay itself. I know you think you have a known good relay, but the symptoms suggest otherwise.

 

[optimusprime]

Next time i go to start the car, and while the key is on no 2 of the starter switch , and if i dontt hear the pumps prime ,then i will do a hot wire test with 7 and 8. What sort of job is it to replace the relay holder -the cage that holds the relay and ecu . I would like to get the whole part out to check the wire joints under it .

 

[carat 3.6]

The relay holder has 4 plastic clips holding it in the surround, push paper clips into those to release it and then push the board down through its holder. Once out you can access the two folding covers that hold the contacts in place, pull them out and inspect them one at a time.

 

[optimusprime]

Reason i asked ,, yesterday i went and moved the FPR in the holder,and after this as i said it started like i have never expeiianced before. So now. it could be the fault in a way . When i am on form [feel well enough ] i will pull the battery out, and remove the holder for the FPR .. carat3.6 thanks again .

 

[optimusprime]

carat 3.6 Do you have a metal square shaped switch over vacuum valve like this- with 2 vacuum pipes exiting the top .Could it be the purge valve just a guess .

 

[optimusprime]

carat 3.6 Sorry...i just found it in my manual .I searched high, and low yesterday, for this valve .I never found it .Reason was in the manual it mounted upside down .. evap system yes ?.

 

[carat 3.6]

If I'm honest the one you've pictured looks more like one of the gearbox valves, the evap system valve is usually engine side of the firewall whereas the one you pictured looks battery side.

 

[optimusprime]

carat 3.6 Yes it is located by the battery .

 

[optimusprime]

Carat 3.6 The part is for the EVAP sytem ..this part is making a whering noise .So i do need to test it . Never noticed it before with the heaters on . so i dont know just how long its made the noise . Cars stood for 4 days ..It was a hard start to -day . it was a test to see how it did start ..just as i though not good ...